diff --git a/CHANGELOG b/CHANGELOG
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -1,5 +1,8 @@
 # CHANGELOG
 
+- 0.12.7.3 (2021-10-26)
+    * Bump `attoparsec` dependency upper bound to 0.15
+
 - 0.12.7.2 (2020-12-07)
     * Bump `QuickCheck` dependency upper bound to 2.15
     * Bump `base64-bytestring` dependency upper bound to 1.3
diff --git a/websockets.cabal b/websockets.cabal
--- a/websockets.cabal
+++ b/websockets.cabal
@@ -1,5 +1,5 @@
 Name:    websockets
-Version: 0.12.7.2
+Version: 0.12.7.3
 
 Synopsis:
   A sensible and clean way to write WebSocket-capable servers in Haskell.
@@ -81,7 +81,7 @@
 
   Build-depends:
     async             >= 2.2    && < 2.3,
-    attoparsec        >= 0.10   && < 0.14,
+    attoparsec        >= 0.10   && < 0.15,
     base              >= 4.8    && < 5,
     base64-bytestring >= 0.1    && < 1.3,
     binary            >= 0.8.1  && < 0.11,
@@ -141,7 +141,7 @@
     test-framework-quickcheck2 >= 0.2 && < 0.4,
     -- Copied from regular dependencies...
     async             >= 2.2    && < 2.3,
-    attoparsec        >= 0.10   && < 0.14,
+    attoparsec        >= 0.10   && < 0.15,
     base              >= 4      && < 5,
     base64-bytestring >= 0.1    && < 1.3,
     binary            >= 0.8.1  && < 0.11,
@@ -170,7 +170,7 @@
     websockets,
     -- Copied from regular dependencies...
     async             >= 2.2    && < 2.3,
-    attoparsec        >= 0.10   && < 0.14,
+    attoparsec        >= 0.10   && < 0.15,
     base              >= 4      && < 5,
     base64-bytestring >= 0.1    && < 1.3,
     binary            >= 0.8.1  && < 0.11,
@@ -201,7 +201,7 @@
     websockets,
     -- Copied from regular dependencies...
     async             >= 2.2    && < 2.3,
-    attoparsec        >= 0.10   && < 0.14,
+    attoparsec        >= 0.10   && < 0.15,
     base              >= 4      && < 5,
     base64-bytestring >= 0.1    && < 1.3,
     binary            >= 0.8.1  && < 0.11,
@@ -230,7 +230,7 @@
     criterion,
     -- Copied from regular dependencies...
     async             >= 2.2    && < 2.3,
-    attoparsec        >= 0.10   && < 0.14,
+    attoparsec        >= 0.10   && < 0.15,
     base              >= 4      && < 5,
     base64-bytestring >= 0.1    && < 1.3,
     binary            >= 0.8.1  && < 0.11,